The inter RAT indicates a technology of allowing a mobile station to continuously receive a service, which is currently being used, even when a mobile station is moved from a network, in which the mobile station is registered, to the other RAT cell so as to improve the convenience of a user.
In the 3GPP network, as shown in FIGS. 1A and 1B, system information is transmitted. The system information may be transmitted using a system information block as shown in FIG. 1A or may be transmitted using a measurement control message as shown in FIG. 1B. A base station periodically transmits the system information block to a mobile station such that the mobile station knows information about a cell in which the mobile station is registered and a neighbor cell, for example, radio bearer information, physical channel information, and an attribute such as cell quality, and provides useful information such that the mobile station continuously receives a service from a present cell or the mobile station is moved to a cell having high quality.
In the technology of the 3GPP network, 15, 16 or 18 pieces of system information are respectively defined and used in a Global System for Mobile communication (GSM), a General Packet Radio Service (GPRS) and a Universal Mobile Telecommunication System (UMTS). Table 1 shows system information block types 4 using cell selection and reselection in a system information block used in the UMTS network. As shown in Table 1, the system information includes information elements including an individual parameter and various parameters, for example, cell selection and reselection information.
TABLE 1Information Element/Group nameNeedType and referenceUTRAN mobilityinformation elementsCell identityMandatoryCell identityCell selection and re-MandatoryCell selection and re-selection infoselection info for SIB3/4Cell Access RestrictionMandatoryCell Access Restriction
In the 3GPP network, cell measurement is performed as follows. The mobile station periodically measures the quality of a present cell or a neighbor cell, for example, an intra neighbor cell or an inter RAT neighbor cell, includes a measurement value in a measurement report message, and transmits the measurement report message to the base station. The base station which receives the measurement report message from the mobile station checks the value included in the message, compares the quality of the cell managed by the base station with the quality of the neighbor cell, and determines whether the mobile station shall stay in the present cell or shall be moved to the neighbor cell having the quality higher than that of the present cell. The measurement report message transmitted from the mobile station to the base station may be transmitted to the base station by a periodic method or an event-trigger method.
Currently, in the 3GPP inter-RAT, a technology of supporting mobility between other RAT cells in the same standard, for example, a technology of supporting mobility from a UMTS network defined in the 3GPP to a GSM network was developed.
However, a technology of supporting mobility between other RAT cells in different standards, for example, a technology of supporting mobility between an E-UTRAN network which is provided in the 3GPP and a World Interoperability for Microwave Access (WiMAX) network which is provided in the IEEE has not been developed.